Hob



July 28, 1925'.

E.-BUCVKINGHAM HOB 4 Filed March 15, 1922 2 Sheets-Sheet 1 July 28, 1925.

v E. B UCKlNGHAM HOB Filed March 13,- .1922 2 Sheets-Sheet; 2

Patented July 28; 1925.

} isms UNITED'STATES "PATENT orn cemans nucxmennm, or HARTFORD, CONNECTICUT, ASSIGINORTO PRATT & WHIT- may COMPANY, or NEW YQRILTX. Y.,, A CORPORATION or NEW JERSEY.

HOB.

Application filed March is, 1922. s mi m suse 4 To all whom it may concern:

Be it' known that I, EARLE .BUcKINcHAM, a citizen of the United States, residing at Hartford, in the county of Hartford and State of Connecticut, have invented certain new and useful Improvements in Hobs, of which the following is a specification.

My invention relates to hobs and particularly to hobs for cutting involute gear teeth. One object of my invention is to provide ahob that shall have the tops and'thesides of ,;the teeth so relieved as to permit the grinding of the front cutting faces without changing the contour cut. by them and that shall have true involute helic'oids'formed on the sides of the teeth. Y

Another object of my invention is'to provide a hob that shall have the teeth formed in a thread by either straight or inclined relieved and i flutes, the front cutting faces formed on the teeth by thefl flutes being either radiall or n0n-radially arranged and the sides an of true involute helicoids Another object of vide a hob that shall have undercut teeth formed by straight or inclined flutes, the tops of the teeth being radially relieved and the sides of the teeth being axially relieved and in the form of involute helicoids, and that shall have theside cutting edges of the teeth contour ground in accordance with the lead of the hob thread.

A further object of my invention is to (provide ahob'that shall have teeth forme by either straight or inclined flutes, the teeth having either non-radially or radially arranged cutting faces formed on them by the flutes, the sides of the. teeth being axially the form of true involute helicoids; and the tops of the teeth being so radially" relieved as to maintain the width across the top of each tooth substantially constant. P Moreover, the hob shall not only have the" front cutting faces of. the teeth ground'but also the side cutting edges, the grinding of the/side cutting edges bein very slight and in accordance with the lea of the hob thread.

Thefirst conception of a hob for cutting teeth on gear wheels was a worm wherein an axial section is the same as the rack which is used'as theubasis for vthe gear ,system. Each side of such a worm is formed by a the topsof the teeth being relieved, andthat shall have the sidesof the teeth in the form my invention isto pro-v tool'havi'ng a straight cutting edge making a predetermmed angle with a plane perfipendicular to the blank axis and extending along a line passing through the blank axis. The straight cutt ng edge is assumed to be revolved and advanced with a uniform lead.

The intersection of the surface so formed with a plane perpendicular to-the blank axis is an Archimedes spiral and not an mvolute as in a hob constructed in accord ance with my invention; A hob so formed will not cut i'nvolute teeth on a gear wheel with the accuracy of a hob which is formed in accordance with my invention and is provided with teeth, the sides of which are true nvolute helicoids.

When a hob has been -formedby a radial- 1y arranged, cutting edge, j'as above set forth, it is difficult to grind and ma'ntain the surfaces f the sides of the hob eeth.

It is well known that-itf is not possible to accurately grind a continuous screw thread with any de cc of accuracy unless the lead of the threa is very small.-' The .reason for the difiiculty in grinding th screw thread is the inabllity o a grinding wheel to cut along-the same cutting line by which the thread is formed. If it is difficult ,to' grind a continuous screw thread, it is apparent that areheved screw thread which is attempted on the sides ofthe hob teethis even' more diflicult to. grind Therefore, in grind-' ing screw thread hobs, it is apparent two errors are introduced, the theoretical error of the surface and the error effected in at- ,tempting to grind relieved-screw threads.

Although a screwthread hob formedin the above indicated manner will approximately'cut true involute gear teeth, it'is a very difiicult matter,-as above set forth, to grind the side surfaces of the hob teeth. During the hardening process, the teeth of a hob are more or less distorted. Accord ingly, it is necessary to grind the teeth of the hob, if gear 'teeth are to be cut with prec'lsion, It is diflicu'lt to grind the side screw surfaces of a hob formed in the above indicated-manner inasmuch as there is no tan-' gent plane along the cutting used to form a screw surface.

' In a hob constructed in accordance edge which is with my invention, the side surfaces of the teeth are relieved in the form of true involute helicoids. The cutting edges ofthe sides of the teeth are contour ground in a manner f is generally set at an angle. with respect to.

, straight flutes eifect a more even cutting ac- ..tiori by the teeth. Non-radially arranged 'to be hereinafter set forth. A hob, constructe'd in accordance'with my invention, may have teeth formed thereon by either straight or helicalfiutes and the cutting faces formed on the teeth by the flutesmay be either radially arranged or non-radially arranged, The straight-flutes are preferred in manufacturing a hob inasmuch as. the hob the Work being operated on and accordingly or undercutteeth are preferred-by reason of the.sharper cutting action effected by them.- The tops of the teeth are radially relieved to such an extent 1 that the width on top of each tooth is maintained substantially constant;

Reference may be had to my copending I application Serial N0. 543,4:03 filed March 13,1922, in which is disclosed methodsfor forming hobs having teeth provided with In forming a hob from a blank in accord ably first formed on a blank by mea'nsof ay 7 suitable formed milling cutterl The thread so formed does not have true involute helicoidal surfacesbut has surfaceswhich are: approximately involute helicoids.

involute helicoidal surfaces. such applicationis disclosed more fully the advantages of an involute helicoidal surface in constructing a hob.

- Hobs, which are formed in accordance withqmy invention, are particularly adapted to form involute teeth on gear Wheels but are not necessarily limited to such operation.

Hobsmay be formed in accordance -with'my invention for cutting screw threads, threads on taps and worm threads," and moreover,

. for performing various other similar operations.

ance with my invention, a thread is preferthread is cut to true helicoidalsurfaces by straight cutting edges which are tangent to the base cylinder of the desired involute helicoid and make a predetermined angle withplanes perpendicular to the :blank axis.

'- cylinder of the desired involute on opposite One cutting edge servesto cut one side of the thread Whereas theother cuttin edge serves to cutthe other-side of the t read.

. Such cutting edges may, if so desired, op-

erate simultaneously. on the blank. When operating simultaneously on the blank, the cutting edges are located in the angular position above set forth and. tangent to the base sides of the blank axis, If so desired, the same cutting tool may be utilized for cutting true involute helicoidal surfaces on each side of the thread. In such case one side "of the blank thread is'first cut to a true involute helicoid and then the position of the blank is reversed and the other-side of the thread is cut to a true involute helicoid by the same.

cutting tool and the same straight cutting Moreover, in

Such

edge. Upon cutting the sides of "the thread 'to true involuteh elicoids, suitable flutes-are cut on'the blank through the thread. Such flutes may befaxial or spiral as desired. The inclination of the spiral flutes may be in either direction, as desired, according to the character of the work being operated 011.

Moreover, the cutting faces of the; teeth,

which-are formed by the flutes, may be ra dially or non-radially arranged, as desired It shouldalso be noted that the thread which is formed on the blank may be a rightrhand' or aleft-hand thread, as desired.

It is customary tdprovidestraight flutesin order to give a more even'cutting action.

However, straight flutes will not givesuch a smooth cutting actionif the hob is setsquare Withthe work or'the generating rack.- The hob may be set at any'desired angle relative to the work; The'fiutes should also be formed on thehob inaccordanc'e With the helix angle or lead on the hob. If the helix angle of the hob is relatively large, the use-of straight flutes will result-in a blunt cutting edge on one side of each hob tooth and a relatively acute angle on the other side ofeach tooth. In such case, it is necessary to .usehelical cutting fluteswhich will be substantially perpendicular to the helix'of-thehob in order'to maintain suitable cutting edges. 7

Upon formingof teeth on the hob by cutting flutes through the thread, the sidefcutting edges of the teeth are'axially relieved and the-top cutting edges are radially ref lieved. The axial reliefon theteeth is' preferably effected by means of a formed lathe tool which is matched to the form of hob teeth must lee-radially relieved to such.

an extent that the width of-the teeth at the topqis approximately uniform. {When axial relief is employed, it is apparent the hob teeth must be lengthened somewhat 'so that the bottom of the fines will clear the outside diameter of the somewhat worn.

After hardening, the front cutting faces of the teeth are-ground in accordance wlth the inclination of the flutes and preferably gear blank when the hob is Upon I completion 1 the side cuttingedge'sare so ground as to make very little or slightfidrag. It, of

course,- will he. preferable to grind the side relieved surfaces but such operation is some- What expensive and a slight contour grinda ing of the side cutting edges produces satisfactory results.

The side cutting edges are ground to true involute-helicoids having the same lead as the lead on the hob thread. Inasmuch as the sides of the teeth have been axially relieved to an appreciable. extent, it is ap.-,

parent tliecontour grinding of the side cutting edges will produce 'onlyxa 'very narrow ribbon of ground surface on the sides of each tooth. ,Such ribbon will be so narrow as not to produce any appreciable lag' or drag. The front cutting faces of the teeth should be ground inthe usual manner in conformity with the direction of the flutes end elevational views of a hob constructed in a accordance with my invention.

Figs. 3 and 4 are respectively side and end elevational views of a hob having teeth provided with radially arranged cuittingfaces formed by inclined flutes. I

Fig. 5 is a diagrammatic view showing the position of theygrinding wheel for contour grinding one side cutting edge.

Figs. 6 and 7 are diagrammatic views showing the positions of a formed lathe tool for axially relieving hobs having teeth provided with radially arranged cutting faces and teeth provided with non-radially .arranged cuttin faces;

Figs. 8 an '9 are respectively side and end elevational views showing a hob having radially arranged'cutting faces formed by straight flutes. i

Figs. 10 and 11 are respectively side and endelevational views of a hob having nonradially arranged cutting faces formed by inclined flutes.

.Referring to Figs. 1 and 2' of the drawings, a hob 1 is shown having teeth 2 formed in a continuous thread by means of straight flutes 3. Non-radially arranged cutting faces 4: are formed on the teeth by the flutes 3. The sides 5 of the teeth 2 are in the form of true involute helicoids and are relieved. by these-called axial relief. The tops of theteeth ;are relieved along lines extending backwardly' and inwardly from the front cutting faces by the so-called radial relief. The tops of the teeth are radially relieved to suchan extent that the width of thetop of each tooth is maintained substantially constant. By so forming the teeth ona hob, it is possible to grind the front cutting faces 4 without changing the shape of the vteeth cut by the hob.

In a hob of the above indicated character,

it is necessary to increase the height of the tooth in front in order to prevent interference between the work and thebottom of the flutes when the tooth is ground back somewhat. Narrow-ribbons of ground surface 7 are formed on the sides of each-tooth backof the side cutting edges. The narrow ribbon of ground surface on each side of the teeth has alead} corresponding 'to'the lead of the hob thread and differing from the lead of either of the involute helicoid on the sides of the teeth. Referring to Fig. 2 of the drawings, a portion of an involute is shown on the sides of two of the teeth. In hobs constructed in accordance with my invention and haying teeth provided with sides having true involute helicoids, a section perpendicular to the axis of the hob will always show involutes. Although a hob having a right-hand thread-is shown in Figs. 1 and 2 of the drawings, it is to be understood that such'hob may have a left-hand thread if so desired.

ings, a hob 8 is shown having teeth 9 formed Referring to Figs. 3 and 4 of the drawin a continuous thread by means of; helical flutes 10. The front cutting faces 11 of the teeth are radially arranged as shown in Fig. 4 of the drawings. The sides 12 of the teeth 9 are relieved by the so-called axial relief and are in the form of true involute helicoids. The tops 13 of the teeth are relieved by the so-called radial relief and to such an extent as to maintain the widthof the teeth on top substantially constant. The front cutting faces 11 of the teeth are ground and a narrow ribbon 14 is ground on the side of each tooth adjacent to the front cutting edge. Such narrow ribbons of ground sur-- "faces on the sides of the teeth are unrelieved and have a. leadcorresponding to the lead of the hob thread. The width of the ribbon does not exceeda thirty-second of an inch andaccordingly does not produce any appreciable drag on'the hob when it is operating on apiece of work. The hob. is sharp ened b grinding the front cutting faces 11 in con ormity'with the flutes 10. -When the front cutting faces are ground back beyond the narrow ribbon of ground surfaces on the.

sides'of the teeth, it is necessary to again contour grind the. sides'of the teeth. A hob shown in Figs. 3 and 4 may be provided with a left hand thread if so'desired.

Referring. to Fig. 6 of the drawings, a hob 15 is. shown having teeth 16 provided with radially arranged cutting faces 17, which are similar to the cutting faces on the hob shown in Figs. 3. and 4 of the drawings.

terclockwise direction as indicated by the arrow. A cutting tool 18 is shown-in engagement with one 'ofathe teeth 16 and having a cutting edge located on a radial line. The cutting edge is matched to one side of a -The hob 15 is assumed to rotate in a coun- 1 tooth which has unrelieved involute helicoidal sides. With the; cutting tool 18 and the hob insuch position, the sides ofthe teeth may be relieved in the customary and usual manner. thread may be formed on the blank prior to the relieving operation either by the methods disclosedin my copending application, Serial No. 548,403 above referred toor by the method disclosed in the pending application of Ernest Wildhaber, Serial. No.

' 543,385 filed March 13, 1922. w

' the tool 26 is" shown parallel to one cut- Referring to Fig. 5 of the drawings, a see I tion of a portion of a hob 20 is s'hown'in engagementwiththe flat surface of a grinding wheel. 21. By means of such a grinding wheel, the contour grinding of the side outting edges of the teeth is effected. The contour'grinding of the side cutting edges of the teeth may be .also effected by a conical grinding wheel in the manner set forth in the application, Serial l lo.5 l3,385 of-Ernest WVildhaber.

Referring'to Fig. 7 of the drawings, a

hob 23 is shown having teeth 24 provided with non-radially arranged cutting faces 25.. A cutting tool 26 is shownin position for relieving the involute helicoidal sides of the teeth. The hob is assumed to rotate in a counter clockwise direction as indicated by the arrow. The cutting edge of ting face of the teeth '24 and moreover is ground to match the side of the tooth with which it is in engagement.- In this regard, .it ,will be noted the cutting edge of thetool 26 is located a distance above the axis of the hob equal to the radius of the so called undercut circle With'thelhob 23' and the cutting tool26 in the position above described, the relieving'of the sides of the teeth is effected inthe' customary. and usual manner.' The method disclosed in Figs. 6

' and 7 of the drawings is only one method of relieving teeth having true involute heli- 'coidal sides. It is to be. understood that other methods such for example as the methods disclosed in the application of Ernest Wildhaber, Serial No. 543,385 above :re-' ferred to may be utilized. In relieving the teeth in accordance with the method disclosed in Figs; 6 and 7 of the drawings, the flutes may be straight or may be inclined in either direction and moreover the hob may-have 'elther right-hand or leIt-hand threads.

Referring to Figs. 8 and 9 of the draw.- ing's, a hob 28 is shown providedwithteeth 29, which are formed in a continuous thread by means of straight flutes '30. The front cutting faces 31'of the teeth, which are formed by the flutes 30, are radially arranged as shown in Fig. 9 of the drawings. The sides 32 of the teeth are in the form of true involute helicoids and are relieved A true involute helicoidal' by the so-called axial relief. The tops 33' of the teethare relieved by the so-called radial relief and are relieved to such an extent as to maintain the width of the teeth on top substantially constant. Narrow riblocus 34 of unrelieved ground surfaees are'.

will be noted that'the hob. shown in Figs.

8 and 9 differs from the hob shown in. Figs. '1 and 2 chiefly in. the arrangement ofthe front cutting faces of the teeth. The hob handed thread if so desired.

In Figs; 10 and 11 of-the drawings,-a

hob EEG is shown having teeth 37 formed in a cont nuous thread by means of helical shown in'Figs. -8 and 9 may have a left'.

flutes-38- The sides 39 of the teeth are-in l vthe form of'true involute heli eoids and are relieved by these called axial relief. The tops 40 of the teeth are radially relieved to such an extent that the width of the tops of the-teeth issubstantiallyconstant. Thus, the teeth may be ground on the front cutting faces without changing the contour; of the teeth out ;by the hob. The height-of the teeth' is increased somewhat in-order to prevent interference between the work and the bottom of the'flutes when the'teet-h are ground back somewhat. bons 41 of unrelieved surfaces are ground back of the side cutting edges of the teeth.

I Such narrow ribbons are in the form of true involute helicoids having the lead of the hob thread. 1 r y It will be understood that such changesand modifications may be made in my inven tion as fall within the limits of the appendedclaims.

' l Vhat I claim is: Y r

lfA hob, comprising teeth arranged in' rows, the side surfaces of the teeth being axially relieved and in theform; of helicoids,

whereby the effective-contour behind-the cessivesurfaces of intersection inclined simi: larly to the lnitial cutting face.

2. A hob comprising teeth having non- Narrow ribif cutting face of each tooth isthe same at sucradially arranged cutting faces,the side surfaces of the teeth being axially relieved and 1 in'the form ofhelicoids so that the effective. contour behind each cuttlng face 1s the same at successive surfaces of intersection 1n-' clined similarly to the initial. cutting face,

whereby the teeth may be ground on the front cutting faces without changing the effective contour cut thereby.

A 3. A hob, comprising teeth jhaving nonradially arranged cutting faces, the side so 1'- eifective contour behind each cutting face is the same at successive surfaces of intersection inclined similarlyto' the initial cutting face, whereby the" teeth may be ground.

on the front cut-ting faces without changing the effective contour cut thereby.

4. A hob, comprising teeth arranged in of the teeth being formed byv flutes each of which is located in a plane including the hob axis, the tops. of the teeth being radially relieved, and the side surfaces of the teeth being axially relieved and in the form of involutehelicoids so that the effective contour behind each cutting face is the same at successive surfaces of' intersection inclined similarly to the initial. cutting face,

whereby the teeth may be ground on the front cutting faces without changing the effective contourcut thereby;

5. A hob, comprising a thread having teeth formed therein by flutes, the tops and the sides of said teeth being. relieved, and the side surfacesof the teeth being inv the form of involute helicoids.

6; A hob, comprising a teeth formed therein by flutes each of which is located in a plane including the hob axis, the tops andthe sides .of the teeth being relieved and the'side surfaces of the teeth being'in the form of involute helicoids;

' 7. A hob, comprising a thread having'undercut teeth formed therein by flutes each of .which is located in a plane including the hob axis, the-tops and sides of the teeth being'relieved and the side surfaces of the teeth being in the form ofhelicoids, whereby the teeth may be ground on the frontcutting faces without changing the effective contour cut thereby.

8. A hob, comprising athread having undercut teeth formed therein byfluteseach of which is located in a plane including the hob axis, the tops and the sides of the teeth being relieved andthe side surfaces of the teeth being in the form of involute helicoids.

hob axis, the tops of the teeth being radially relieved and the side surfaces of the teeth being axially relieved and in the. form-0f helicoids, whereby the teeth may be ground on the front cutting faces without changing the effective contour cut thereby.

10. A hob, comprising a thread havingundercut teeth formed therein by flutes each of which is located in a plane including the hob axis, the tops of the teeth being radially relieved and'the side surfaces of the "thread havingteeth being axially relievedand in the form- 1 of involute helicoids.

faces of the teeth being axially relieved and. in the form of involute helicoids-so that the '11- A hob, comprising a .thread having teeth formed therein by flutes each of which 'islocated in a plane including the hob axis,

the tops and the sides ofthe teeth being relieved, the sidesu'rfaces of theteeth being in the form of helicoids-and the side. cutting edges of the teeth being ground in conformity withthe lead ofthe thread and the con-' tour of the teeth. v the form of a thread, the front cutting face-s 12. A hob, comprising a thread havin teeth formedthereinbyflutes, the tops an the sides of'the teeth being relieved, the'side surfaces of the teeth being in the form of involute helicoids, and the side cutting edges of the teeth being ground in, conformity with the lead of the thread and the contour of the teeth.

13. A hob, comprising thread having undercut teeth formed therein by flutes each of which is located ina plane includingthe hob axis, thetops of the teeth being radially relieved, the side surfaces of the teeth being axially relieved and in the form of helicoids and'the side cutting edges of the teeth being ground in conformity with the lead of the. 1

hob axis, the tops ofthe teeth being radially I relieved, the side surfaces of the teeth being axially relieved and in the, form of. involute helicoids, and the side cutting edges of the teeth being ground in conformity with the lead of the thread and the contour of the l teeth; x A

15. A hob, comprising a thread having 1 teeth formed therein by flutes eachof which is located in a plane including the hob axis, the frontcutting faces "of the teeth being non-radially arranged, the tops' of said teeth being radially relieved, the side surfaces of said teethbeingaxially relieved and in the form of involutehelicoids, andth'e side cutting edges of the teeth being ground inconformity with the lead ofthe thread and the contour of the sides of the teeth.

16. A hob, comprising teeth arranged to form a thread, the side surfaces of the teeth being axially relieyed and in the form of helicoids so that the effective contour behind each cutting face is the same at successive surfaces of intersection inclined similarly to the initial cutting face, and the side cutting edges of the teeth being ground in conformity with the lead of the thread and the contour of the sides of the teeth.

17. Ahob, comprising teeth arranged in the form of; a thread and having non radially arranged cutting faces, the side surthe same atsu'ccessive surfaces-0f intersection inclined similarly to the initial cutting face, and the side cutting edges of the teeth beingof the teeth. r v 18. A'hob with curved sided threads having one or more helical series of teeth'whose side faces comprise helicoidal surfaces of uniform lead at all diameters of the hob. 10 ground in conformity with the-lead i i 5 of the thread and" the cqntoui ofthe sides In testimony whereof, I heret0' aflix my signature.

EARLE- BUCKINGHAM. 

